Protective thin film coatings ranging in thickness from a few nanometers to several micrometers are used to protect surfaces that are in contact and sliding. These coatings can be found in applications such as magnetic storage hard disk drives, compressors, engines, biological devices and many others. Compressors and similar industrial equipment comprise moving parts that are subject to constant wear and fatigue because of prolonged surface contact and motion. Without protective treatment of the surfaces, equipment that utilizes internally moving parts can suffer from catastrophic failures. Next-generation compressors are being designed to withstand stringent contact and operating conditions, including oil-less or low-lubricant operation. Surface treatments/coatings are key to improving performance and durability for these applications since advanced ultra-low wear and inexpensive coatings would substantially reduce operating costs.
In recent years, great efforts have been made in the formulation of solid lubricants and solid lubricant coatings to achieve desired levels of performance or durability that conventional materials and lubricants cannot provide. Numerous techniques and diverse materials have been used to develop new solid coatings. For simplicity, coatings can be classified into two broad categories—soft coatings (hardness <10 GPa) and hard coatings (hardness >10 GPa). Conventionally, hard coatings such as diamond-like carbon (DLC), Ti—N and WC/C are synthesized through physical vapor deposition (PVD) and chemical vapor deposition (CVD) techniques. These are thought to be effective in preventing both abrasive and adhesive wear of metal sliding contacts. However, hard coatings are relatively expensive and are difficult to coat on substrates with low surface energies, high roughness, and/or complex geometries. They also often wear out the counterface they slide against due to their relatively high hardness.
Due to these concerns with hard coatings, recent attention has focused on soft, thermoplastic-based polymers such as polytetrafluoroethylene (PTFE) and polyether ether ketone (PEEK), which show relatively low friction coefficient and self-lubricating properties. Significant work has been performed with bulk polymeric blends based on PTFE and PEEK for high bearing applications. The main advantages of the polymeric-based coatings are their relatively low cost and simple substrate surface conditioning (i.e., no need for expensive surface preparation before coating). Despite the improvements in wear offered by bulk polymer blends, they are not likely to replace critical components in compressors (and other machinery) since polymeric coatings still exhibit the following problems:                their wear rate is still high (compared to hard coatings);        because they rely heavily on the interaction between the PTFE/PEEK wear debris/solid lubricant (debris film) and the substrate for surface protection, in the presence of lubricant they may become ineffective;        the addition of hard particles in these mixtures scratches the counterface, thus creating excessive abrasive wear;        the wear debris likely contains hard particles that can damage downstream machinery; and        they often have low glass transition temperatures (Tg<150° C.), which limits the operating temperature.        
However, little work has been done on new high bearing polymeric-based coatings that would overcome the shortcomings highlighted above, which are highly desirable in most industrial applications.